The present invention relates to a titanyl phthalocyanine composition having a new crystal form, a process for its manufacture and its use as a highly photosensitive material for electrophotography.
It is well known that phthalocyanines, particularly metallo-phthalocyanines, have an excellent photoconductive property and some of them have been used for preparation of electrophotographic photosensitive materials. Recently, high definition and high speed electrophotographic type optical printers that use a laser beam or a light emitting diode as the light source have been in widespread use accompanying advances in the nonimpact printing technology, and an active development in photosensitive bodies that can meet the requirements of these devices is under way.
Particularly when a laser beam is used as a light source, there is a need to obtain a photosensitive material having a photosensitivity up to a near infrared region. It is because mostly a semiconductor laser diode is used owing to the merits of compactness, cheapness and simplicity, but their oscillation wavelength is now limited to a relatively longer wavelength range of a near infrared region. Accordingly, it is not appropriate to use conventional photosensitive materials, which have been used for electrophotographic copying machines and have a sensitivity in a visible region, with a semiconductor laser light source.
It is known that some organic materials satisfy the need as described above mentioned. They are, for example, squaric acid methine dyes, indoline dyes, cyanine dyes, pyrylium dyes, polyazo dyes, phthalocyanine dyes, naphthoquinone dyes, etc. At present, however, the squaric acid methine dyes, indoline dyes, cyanine dyes and pyrylium dyes enable to obtain a longer wavelength range but are lacking in a utilizable stability, that is, repeating property; the polyazo dyes are difficult to obtain a longer wavelength range and also have disadvantages in their production; and naphthoquinone dyes have a problem in their sensitivity.
On the other hand, the phthalocyanine dyes have spectrum sensitivity peaks in the long wavelength region of not less than 600 nm, have high sensitivities and further change their spectrum sensitivities in accordance with the kinds of their center metals and their crystal forms. They are therefore considered as suitable for dyes for use with a semiconductor laser light source, and so research and development of phthalocyanine dyes have been intensively conducted.
Among the phthalocyanine compounds studied hitherto, particularly as those showing high sensitivities in the long wavelength region of not less than 780 nm, there may be mentioned, x-type non-metalo-phthalocyanine, E-type copper phthalocyanine, vanadyl phthalocyanine, etc.
In order to obtain a higher sensitivity, it has been attempted to use a vacuum evaporated film of phthalocyanine as a charge generation layer to produce a laminated type photosensitive material. In effect, some phthalocyanines of relatively high sensitivities have been obtained by using metals of groups IIIa and IV of the periodic table as center metals. Such metalo-phthalocyanines are described in, for example, Japanese Patent Laid-open Nos. 211,149/82, 148,745/82, 36,254/84, 44,054/84, 30,541/84, 31,965/84, 166,959/84, etc. Such organic photosensitive materials as above, however, necessarily become expensive, since the production of the vacuum evaporated film requires a high vacuum discharge apparatus and thus a high cost of installation.
It has also been attempted to use a resin dispersion layer of phthalocyanine, in place of said vacuum evaporated film of phthalocyanine, as a charge generation layer and to make a coating of a charge transfer layer thereon to produce a composite type photosensitive material. As for such composite type photosensitive material, there may be mentioned, for example, the photosensitive material using non-metalo-phthalocyanine as described in Japanese Patent Laid-open No. 182639/83 and that using indium phthalocyanine as described in Japanese Patent Laid-open No. 155851/84. These two are relatively high sensitivity photosensitive materials, but the former is disadvantageous in that its sensitivity is rapidly reduced in a long wavelength region of not less than 800 nm, and the latter is disadvantegeous in that its sensitivity is not sufficient for utilization, when the charge generation layer is produced by means of the resin dispersion system.
It has also been attempted in these days to use titanyl phthalocyanines having relatively high sensitive electrophotographic properties as described in Japanese Patent Laid-open Nos. 49,544/84,, 23,928/86, 109,056/86 and 275,272/87. According to this literature, it is understood that their properties are different owing to their crystal forms and that in order to produce these various crystal forms, special purification and special solvent treatment are required. Further, the solvent to be used for such treatment is one that is different from the solvent to be used in forming the dispersion coating film. It is because the various crystals to be formed have a tendency to easily grow in the solvent for the crystal growing treatment. Thus, if such solvent is used also as the solvent for the coating, it is difficult to control the crystal form and the particle size. This causes low stability of the coating material and eventually the electrostatic properties are significantly damaged. Therefore, ordinarily in the treatment of forming the coating material, a chlorine series solvent such as chloroform, which does not substantially promote the crystal growth, is used. This solvent however does not always show a good dispersion property for the titanyl phthalocyanine, and thus causes some problems in the dispersion stability of the coating material.